scholarly journals Forest carbon sink neutralized by pervasive growth-lifespan trade-offs

2020 ◽  
Vol 11 (1) ◽  
Author(s):  
R. J. W. Brienen ◽  
L. Caldwell ◽  
L. Duchesne ◽  
S. Voelker ◽  
J. Barichivich ◽  
...  
Keyword(s):  
Tree Growth ◽  
Tree Mortality ◽  
Carbon Sink ◽  
Growth Stimulation ◽  
Forest Carbon ◽  
System Model ◽  
Earth System ◽  
Canopy Tree ◽  
Trade Offs ◽  
Almost All

Abstract Land vegetation is currently taking up large amounts of atmospheric CO2, possibly due to tree growth stimulation. Extant models predict that this growth stimulation will continue to cause a net carbon uptake this century. However, there are indications that increased growth rates may shorten trees′ lifespan and thus recent increases in forest carbon stocks may be transient due to lagged increases in mortality. Here we show that growth-lifespan trade-offs are indeed near universal, occurring across almost all species and climates. This trade-off is directly linked to faster growth reducing tree lifespan, and not due to covariance with climate or environment. Thus, current tree growth stimulation will, inevitably, result in a lagged increase in canopy tree mortality, as is indeed widely observed, and eventually neutralise carbon gains due to growth stimulation. Results from a strongly data-based forest simulator confirm these expectations. Extant Earth system model projections of global forest carbon sink persistence are likely too optimistic, increasing the need to curb greenhouse gas emissions.

scholarly journals Evaluating simplified chemical mechanisms within present-day simulations of the Community Earth System Model version 1.2 with CAM4 (CESM1.2 CAM-chem): MOZART-4 vs. Reduced Hydrocarbon vs. Super-Fast chemistry

2018 ◽  
Vol 11 (10) ◽  
pp. 4155-4174 ◽  
Author(s):  
Benjamin Brown-Steiner ◽  
Noelle E. Selin ◽  
Ronald Prinn ◽  
Simone Tilmes ◽  
Louisa Emmons ◽  
...  
Keyword(s):  
Computational Cost ◽  
Earth System Model ◽  
Chemical Mechanism ◽  
System Model ◽  
Earth System ◽  
Chemical Mechanisms ◽  
Trade Offs ◽  
Community Earth System Model ◽  
Time Periods ◽  
Fast Mechanism

Abstract. While state-of-the-art complex chemical mechanisms expand our understanding of atmospheric chemistry, their sheer size and computational requirements often limit simulations to short lengths or ensembles to only a few members. Here we present and compare three 25-year present-day offline simulations with chemical mechanisms of different levels of complexity using the Community Earth System Model (CESM) Version 1.2 CAM-chem (CAM4): the Model for Ozone and Related Chemical Tracers, version 4 (MOZART-4) mechanism, the Reduced Hydrocarbon mechanism, and the Super-Fast mechanism. We show that, for most regions and time periods, differences in simulated ozone chemistry between these three mechanisms are smaller than the model–observation differences themselves. The MOZART-4 mechanism and the Reduced Hydrocarbon are in close agreement in their representation of ozone throughout the troposphere during all time periods (annual, seasonal, and diurnal). While the Super-Fast mechanism tends to have higher simulated ozone variability and differs from the MOZART-4 mechanism over regions of high biogenic emissions, it is surprisingly capable of simulating ozone adequately given its simplicity. We explore the trade-offs between chemical mechanism complexity and computational cost by identifying regions where the simpler mechanisms are comparable to the MOZART-4 mechanism and regions where they are not. The Super-Fast mechanism is 3 times as fast as the MOZART-4 mechanism, which allows for longer simulations or ensembles with more members that may not be feasible with the MOZART-4 mechanism given limited computational resources.

scholarly journals Description of the MIROC-ES2L Earth system model and evaluation of its climate–biogeochemical processes and feedbacks

2019 ◽  
Author(s):  
Tomohiro Hajima ◽  
Michio Watanabe ◽  
Akitomo Yamamoto ◽  
Hiroaki Tatebe ◽  
Maki A. Noguchi ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Nitrogen Cycle ◽  
Carbon Sink ◽  
Coupled Model ◽  
System Model ◽  
Climate Response ◽  
Earth System ◽  
Model Intercomparison ◽  
Transient Climate Response ◽  
Intercomparison Project

Abstract. This study developed a new Model for Interdisciplinary Research on Climate, Earth System version2 for Long-term simulations (MIROC-ES2L) Earth system model (ESM) using a state-of-the-art climate model as the physical core. This model embeds a terrestrial biogeochemical component with explicit carbon–nitrogen interaction to account for soil nutrient control on plant growth and the land carbon sink. The model’s ocean biogeochemical component is largely updated to simulate biogeochemical cycles of carbon, nitrogen, phosphorus, iron, and oxygen such that oceanic primary productivity can be controlled by multiple nutrient limitations. The ocean nitrogen cycle is coupled with the land component via river discharge processes, and external inputs of iron from pyrogenic and lithogenic sources are considered. Comparison of a historical simulation with observation studies showed the model could reproduce reasonable historical changes in climate, the carbon cycle, and other biogeochemical variables together with reasonable spatial patterns of distribution of the present-day condition. The model demonstrated historical human perturbation of the nitrogen cycle through land use and agriculture, and it simulated the resultant impact on the terrestrial carbon cycle. Sensitivity analyses in preindustrial conditions revealed modeled ocean biogeochemistry could be changed regionally (but substantially) by nutrient inputs from the atmosphere and rivers. Through an idealized experiment of a 1 %CO2 increase scenario, we found the transient climate response (TCR) in the model is 1.5 K, i.e., approximately 70 % that of our previous model. The cumulative airborne fraction (AF) is also reduced by 15 % because of the intensified land carbon sink, resulting in an AF close to the multimodel mean of the Coupled Model Intercomparison Project Phase 5 (CMIP5) ESMs. The transient climate response to cumulative carbon emission (TCRE) is 1.3 K EgC−1, i.e., slightly smaller than the average of the CMIP5 ESMs, suggesting optimistic model performance in future climate projections. This model and the simulation results are contributing to the Coupled Model Intercomparison Project Phase 6 (CMIP6). The ESM could help further understanding of climate–biogeochemical interaction mechanisms, projections of future environmental changes, and exploration of our future options regarding sustainable development by evolving the processes of climate, biogeochemistry, and human activities in a holistic and interactive manner.

scholarly journals Drivers of multi-century trends in the atmospheric CO<sub>2</sub> mean annual cycle in a prognostic ESM

2017 ◽  
Vol 14 (6) ◽  
pp. 1383-1401 ◽  
Author(s):  
Jessica Liptak ◽  
Gretchen Keppel-Aleks ◽  
Keith Lindsay
Keyword(s):  
Climate Change ◽  
Land Use ◽  
Annual Cycle ◽  
Carbon Sink ◽  
Atmospheric Co2 ◽  
System Model ◽  
Earth System ◽  
Co2 Fertilization ◽  
Cycle Amplitude ◽  
The Mean

Abstract. The amplitude of the mean annual cycle of atmospheric CO2 is a diagnostic of seasonal surface–atmosphere carbon exchange. Atmospheric observations show that this quantity has increased over most of the Northern Hemisphere (NH) extratropics during the last 3 decades, likely from a combination of enhanced atmospheric CO2, climate change, and anthropogenic land use change. Accurate climate prediction requires accounting for long-term interactions between the environment and carbon cycling; thus, analysis of the evolution of the mean annual cycle in a fully prognostic Earth system model may provide insight into the multi-decadal influence of environmental change on the carbon cycle. We analyzed the evolution of the mean annual cycle in atmospheric CO2 simulated by the Community Earth System Model (CESM) from 1950 to 2300 under three scenarios designed to separate the effects of climate change, atmospheric CO2 fertilization, and land use change. The NH CO2 seasonal amplitude increase in the CESM mainly reflected enhanced primary productivity during the growing season due to climate change and the combined effects of CO2 fertilization and nitrogen deposition over the mid- and high latitudes. However, the simulations revealed shifts in key climate drivers of the atmospheric CO2 seasonality that were not apparent before 2100. CO2 fertilization and nitrogen deposition in boreal and temperate ecosystems were the largest contributors to mean annual cycle amplification over the midlatitudes for the duration of the simulation (1950–2300). Climate change from boreal ecosystems was the main driver of Arctic CO2 annual cycle amplification between 1950 and 2100, but CO2 fertilization had a stronger effect on the Arctic CO2 annual cycle amplitude during 2100–2300. Prior to 2100, the NH CO2 annual cycle amplitude increased in conjunction with an increase in the NH land carbon sink. However, these trends decoupled after 2100, underscoring that an increasing atmospheric CO2 annual cycle amplitude does not necessarily imply a strengthened terrestrial carbon sink.

scholarly journals Development of the MIROC-ES2L Earth system model and the evaluation of biogeochemical processes and feedbacks

2020 ◽  
Vol 13 (5) ◽  
pp. 2197-2244 ◽  
Author(s):  
Tomohiro Hajima ◽  
Michio Watanabe ◽  
Akitomo Yamamoto ◽  
Hiroaki Tatebe ◽  
Maki A. Noguchi ◽  
...  
Keyword(s):  
Carbon Cycle ◽  
Nitrogen Cycle ◽  
Carbon Sink ◽  
Earth System Model ◽  
System Model ◽  
Climate Projections ◽  
Climate Response ◽  
Earth System ◽  
Transient Climate Response ◽  
Ocean Biogeochemistry

Abstract. This article describes the new Earth system model (ESM), the Model for Interdisciplinary Research on Climate, Earth System version 2 for Long-term simulations (MIROC-ES2L), using a state-of-the-art climate model as the physical core. This model embeds a terrestrial biogeochemical component with explicit carbon–nitrogen interaction to account for soil nutrient control on plant growth and the land carbon sink. The model's ocean biogeochemical component is largely updated to simulate the biogeochemical cycles of carbon, nitrogen, phosphorus, iron, and oxygen such that oceanic primary productivity can be controlled by multiple nutrient limitations. The ocean nitrogen cycle is coupled with the land component via river discharge processes, and external inputs of iron from pyrogenic and lithogenic sources are considered. Comparison of a historical simulation with observation studies showed that the model could reproduce the transient global climate change and carbon cycle as well as the observed large-scale spatial patterns of the land carbon cycle and upper-ocean biogeochemistry. The model demonstrated historical human perturbation of the nitrogen cycle through land use and agriculture and simulated the resultant impact on the terrestrial carbon cycle. Sensitivity analyses under preindustrial conditions revealed that the simulated ocean biogeochemistry could be altered regionally (and substantially) by nutrient input from the atmosphere and rivers. Based on an idealized experiment in which CO2 was prescribed to increase at a rate of 1 % yr−1, the transient climate response (TCR) is estimated to be 1.5 K, i.e., approximately 70 % of that from our previous ESM used in the Coupled Model Intercomparison Project Phase 5 (CMIP5). The cumulative airborne fraction (AF) is also reduced by 15 % because of the intensified land carbon sink, which results in an airborne fraction close to the multimodel mean of the CMIP5 ESMs. The transient climate response to cumulative carbon emissions (TCRE) is 1.3 K EgC−1, i.e., slightly smaller than the average of the CMIP5 ESMs, which suggests that “optimistic” future climate projections will be made by the model. This model and the simulation results contribute to CMIP6. The MIROC-ES2L could further improve our understanding of climate–biogeochemical interaction mechanisms, projections of future environmental changes, and exploration of our future options regarding sustainable development by evolving the processes of climate, biogeochemistry, and human activities in a holistic and interactive manner.

scholarly journals Predicting the variable ocean carbon sink

2019 ◽  
Vol 5 (4) ◽  
pp. eaav6471 ◽  
Author(s):  
H. Li ◽  
T. Ilyina ◽  
W. A. Müller ◽  
P. Landschützer
Keyword(s):  
Carbon Sink ◽  
System Model ◽  
Carbon Uptake ◽  
Prediction System ◽  
Earth System ◽  
Temperature Variations ◽  
The Past ◽  
Predictive Skill ◽  
Decadal Variations ◽  
Ocean Carbon

Strong decadal variations in the oceanic uptake of carbon dioxide (CO2) observed over the past three decades challenge our ability to predict the strength of the ocean carbon sink. By assimilating atmospheric and oceanic observational data products into an Earth system model–based decadal prediction system, we can reproduce the observed variations of the ocean carbon uptake globally. We find that variations of the ocean CO2 uptake are predictable up to 2 years in advance globally, albeit there is evidence for a higher predictive skill up to 5 years regionally. We further suggest that while temperature variations largely determine shorter-term (<3 years) predictability, nonthermal drivers are responsible for longer-term (>3 years) predictability, especially at high latitudes.

scholarly journals Inclusion of ecologically based trait variation in plant functional types reduces the projected land carbon sink in an earth system model

2015 ◽  
Vol 21 (8) ◽  
pp. 3074-3086 ◽  
Author(s):  
Lieneke M. Verheijen ◽  
Rien Aerts ◽  
Victor Brovkin ◽  
Jeannine Cavender-Bares ◽  
Johannes H. C. Cornelissen ◽  
...  
Keyword(s):  
Carbon Sink ◽  
Earth System Model ◽  
Plant Functional Types ◽  
System Model ◽  
Earth System ◽  
Trait Variation ◽  
Functional Types

scholarly journals Field-based tree mortality observations constrain model-projected forest carbon sinks across continents

2021 ◽  
Author(s):  
Kailiang Yu ◽  
Philippe Ciais ◽  
Sonia Seneviratne ◽  
Zhihua Liu ◽  
Han Chen ◽  
...  
Keyword(s):  
North America ◽  
South America ◽  
Tree Mortality ◽  
Net Primary Productivity ◽  
Carbon Sink ◽  
Demographic Data ◽  
Forest Carbon ◽  
Western Coast ◽  
Tropical Regions ◽  
Considerable Uncertainty

Abstract Considerable uncertainty and debate exist in projecting the future capacity of forests to sequester atmospheric CO2. Here we generate spatially explicit patterns of biomass loss by mortality (LOSS) from a dataset (n = 2676) of long-term (1951 to 2018), largely unmanaged forest plots to constrain projected (2015–2099) net primary productivity (NPP), heterotrophic respiration (HR) and net carbon sink in six dynamic global vegetation models (DGVMs) across North and South America, Africa, Asia, and Australia. This approach was motivated by the higher accuracy of field-derived LOSS estimates and the strong relationship among LOSS, NPP, and HR at continental or biome scales. The field observations showed higher values of LOSS in tropical regions (0.53 Kg m− 2 y− 1) than in North America (0.22 Kg m− 2 y− 1). The upscaled gridded LOSS map show hotspots in Southern Asia & Australia, Northwestern South America, and the western coast of North America. The DGVMs overestimated LOSS, particularly in tropical regions and eastern North America by as much as 0.5 Kg m2− y1. The spread of DGVM-projected NPP and HR uncertainties was substantially reduced after constraining the simulations with the observed LOSS patterns. The observation-constrained models show a decrease in the tropical forest carbon sink by the end of the century, particularly across South America (from 2 to 1.3 PgC y1), and an increase in the sink in North America (from 0.75 to 0.97 PgC y1). These results suggest that forest demographic data can be used to constrain land carbon sink projections.

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